1. Field of the Invention
This invention relates to storage tanks having liners, especially storage tanks with plastic liners used for storing compressed gaseous fuels.
2. Description of the Related Art
Pressure vessels are widely used to store liquids and gases under pressure. One growing application of pressure vessels is their use in the storage of alternative fuels, such natural gas or propane, for use in vehicles such as automobiles. Natural gas and propane are increasingly viewed as preferable to gasoline for fueling vehicles. Accordingly, approaches have been devised for converting gasoline-fueled vehicles to natural gas-fueled or propane-fueled vehicles by retrofitting them to use natural gas or propane instead of gasoline. Additionally, new vehicles are currently being built which are designed to operate using natural gas or propane as the fuel source.
Vessels used for storing natural gases and propane preferably are equipped with a plastic liner, which serves to keep the stored gas from leaking. The plastic liner preferably covers the entire interior surface of the pressure vessel, including the neck portion, which defines an access opening for loading fuel. To prevent leakage of fuel at the access opening, an O-ring or other sealing means may be used.
An example of a sealing arrangement initially considered by the inventors is shown in FIG. 3. As shown in FIG. 3, the sealing arrangement includes a plastic liner 300 covering the inner surface 302 of a pressure vessel 304. A nipple portion 306 of the plastic liner 300 covers the inner periphery of the neck region 308 of a polar boss 310. An O-ring 312 abuts against the edge (unnumbered) of the neck region 308 and is urged towards the neck region 308 as fitting body 314 is moved towards the neck region 308 to compress the O-ring 312 therebetween. The fitting body 314 and the polar boss 310 have respective complementary screw-threaded surface regions facing and engaging each other at 316. Rotational movement of the fitting body 314 relative to the polar boss 310 mechanically engages the fitting body 314 to the pressure vessel 304 and seals the fitting body 314 against the nipple portion 306 of the plastic liner 300, with the O-ring 312 interposed therebetween to establish a hermetic seal.
While the design illustrated in FIG. 3 is acceptable under ideal operating conditions, under extreme temperature and pressure conditions, such as those sometimes encountered in harsh climates, the plastic liner 300 tends to contract, causing the liner 300 to move away from the fitting body 314. Separation of the edge of the plastic liner 300 from the polar boss 308 interrupts the hermetic seal created by the O-ring 312, causing fuel, especially in gaseous state, to leak from the pressure vessel 304 to the outside environment.
It would, therefore, be a significant advancement in the art to provide a simple sealing arrangement which, upon engagement of the fitting body to the storage vessel, forms a hermetic seal between the plastic liner and the end fitting that is resistant to high loading pressures and extreme operating temperatures, such as from about -40.degree. C. 40.degree. F.) to about 82.2.degree. C. (180.degree. F.).